The 3rd Generation Partnership Project (3GPP) aims to promote a 3G standard based on an evolved Global System for Mobile Communications (GSM) core network; the 3GPP has designed corresponding protocol specifications for different data services in the 3G system, in which a service area designated by a base station is called a cell. With the change of a geographical location of a mobile subscriber, the UE used by the mobile subscriber will move from a current serving cell to a target serving cell. Such serving cell selection made by UE is called cell reselection; the cell reselection aims to make UE reside in an ideal serving cell, so as to ensure the quality of connection.
Usually, before performing cell reselection, UE needs to first measure a signal quality value Srxlev of a current serving cell, and then decide whether to initiate measurement of a neighbouring cell according to the signal quality value Srxlev and a threshold Sint rasearch/Snon_int rasearch of measurement initiation of the neighbouring cell. The step of UE initiating measurement of a neighbouring cell includes that the UE initiates measurement of a neighbouring intra-frequency cell and measurement of a neighbouring inter-frequency/inter-system cell; the measurement of a neighbouring intra-frequency cell needs to compare the signal quality value Srxlev with the threshold Sint rasearch of measurement initiation of a neighbouring intra-frequency cell; the measurement of the neighbouring inter-frequency/inter-system cell needs to compare the signal quality value Srxlev with the threshold Snon_int rasearch of measurement initiation of a neighbouring inter-frequency/inter-system cell. The technology that UE initiates measurement of a neighbouring intra-frequency cell is already quite mature, so how UE initiates measurement of a neighbouring inter-frequency/inter-system cell becomes a current focus of research.
In the related art, when a signal quality value Srxlev of a current serving cell is smaller than or equal to a threshold Snon_int rasearch of measurement initiation of a neighbouring inter-frequency/inter-system cell, UE initiates measurement of the neighbouring inter-frequency/inter-system cell, wherein the signal quality value Srxlev is obtained by calculation according to formula (1) and formula (2):Srxlev=Qrxlevmeas−Qrxlev min−Pcompensation  (1)Pcompensation=MAX(UE_TXPWR_MAX_RACH−P_MAX,0)  (2)
wherein Qrxlevmeas represents a received power quality value of the current serving cell measured by the UE; Qrexlev min represents the minimum received power quality value of the UE required by the current serving cell, and this value is transmitted to the UE through a system broadcast message; P_MAX represents the maximum transmitted power value of the UE; UE_TXPWR_MAX_RACH represents the maximum transmitted power value of the UE allowed to use on a Random Access Channel (RACH); Pcompensation represents a power compensation quality value needed by the UE when accessing the RACH of the base station to which the current serving cell belongs, and its value is the maximum between UE_TXPWR_MAX_RACH−P_MAX and 0, and this value is transmitted to the UE through a system broadcast message.
In such method of determining whether the UE initiates measurement of a neighbouring inter-frequency/inter-system cell by comparing Srxlev with Snon_int rasearch, the condition for the UE to initiate the measurement of a neighbouring inter-frequency/inter-system cell is very simple, i.e., only Srxlev≦Snon_int rasearch needs to be satisfied; moreover, the value of Snon_int rasearch is not unique, but changes with change of a communication environment. If the value of Snon_int rasearch is relatively large, some pieces of UE which actually do not need to initiate the measurement of a neighbouring inter-frequency/inter-system cell will initiate the measurement of a neighbouring inter-frequency/inter-system cell, which causes unreasonable waste of electric power of these pieces of UE.
Different from the above condition for UE to initiate measurement of a neighbouring inter-frequency/inter-system cell, a patent document, which has a title of a cell selecting device and method in a mobile communication terminal and which has an application number of 200510120052, describes a cell selecting method, wherein UE measures an error rate of messages sent from a base station to which a current serving cell belongs, and reselects a serving cell when the measured error rate is greater than a reference value pre-stored in the UE. Such a technical solution takes into account a situation that a wireless transmission channel changes in real time, but does not take into account a situation that a wireless transmission environment in a network has almost no change and a situation that the UE does not move or moves a little.
In practical application, the situation that UE does not move or moves a little often happens, for example, a mobile subscriber often moves within a small space like in the office or at home. However, even if the UE does not move or moves a little, the UE also initiates the measurement of a neighbouring inter-frequency/inter-system cell, because the mobile subscriber always hopes that the UE used by him/her resides in an ideal serving cell with the best signal quality. If the UE does not move or moves a little, it is indicated that the current serving cell is the one where the UE gets the best signal quality, at which moment however, the UE will still initiate the measurement and search of signal quality of a neighbouring inter-frequency/inter-system cell, which is obviously useless, not only wasting electric power of the UE, but also causing more radiation to the mobile subscriber.